Process for producing an image using a first minimum bottom antireflective coating composition

ABSTRACT

Disclosed is a process for forming an image on a substrate, comprising the steps of: (a) coating on the substrate a first layer of a radiation sensitive, antireflective composition; (b) coating a second layer of a photoresist composition onto the first layer of the antireflective composition; (c) selectively exposing the coated substrate from step (b) to actinic radiation; and (d) developing the exposed coated substrate from step (c) to form an image; wherein both the photoresist composition and the antireflective composition are exposed in step (c); both are developed in step (d) using a single developer; wherein the antireflective composition of step (a) is a first minimum bottom antireflective coating (B.A.R.C.) composition, having a solids content of up to about 8% solids, and a maximum coating thickness of the coated substrate of λ/2n wherein λ is the wavelength of the actinic radiation of step (c) and n is the refractive index of the B.A.R.C. composition.

This application is a continuation of Ser. No. 10/042,878, filed Jan. 9,2002, the contents of which are herein incorporated by reference.

FIELD OF THE INVENTION

This invention relates to the field of antireflective coatings and to aprocess for forming an image on a substrate using an antireflectivecoating composition.

BACKGROUND OF THE INVENTION

In the production of semiconductor devices, an integrated circuitsubstrate is coated with a film of photo patterning resist, exposed toactinic radiation, and developed to define a resist image over theintegrated circuit substrate. The resist image can, for example, includeboth lines and spaces, wherein portions of the photo patterning resistthat are removed form the spaces and the portions that remain form thelines. The resist image is transferred to the integrated circuitsubstrate by modifying the exposed portion of the substrate. Suchmodification may be performed by removal of a portion of the substrateby etching processes, by implantation of atomic species into thesubstrate, or by other methods known to those skilled in the art. Duringsuch processes, the photo patterned resist lines act as a mask toprevent modification of the portions of the substrate underlying theresist lines. Resolution of the image transferred to the substrate isdependent on the resolution of the resist image.

During exposure of a photo patterning resist on an integrated circuitsubstrate, some reflection of the actinic radiation off the integratedcircuit substrate will typically occur. The reflection causes filminterference effects that change the effective exposure intensity withina chip, across the wafer, and from wafer to wafer. Given the variationin effective exposure intensity, an unacceptable amount of line widthvariation typically occurs. This is especially true in modernmanufacturing where laser exposure tools are used as the source of theactinic radiation and reflection is particularly prevalent.

To prevent reflection of actinic radiation into a photo patterningresist, one or more layers of an antireflective coating (A.R.C.) may beprovided between a substrate and a photo patterning resist film. A.R.C.soften include a radiation adsorbing dye dispersed in a polymer binder,however, some polymers exist that contain an appropriate chromophorethat sufficiently adsorbs the actinic radiation (i.e., the chromophoreacts as the dye) such that an additional adsorbing dye is not required.The A.R.C. may be adapted to attenuate a particular wavelength ofradiation used to expose the photo patterning resist by a selection ofsuitable adsorbing dyes or a polymer having suitable chromophores.

The use of an A.R.C. however is not without problems. Once the photopatterning resist film is developed, exposing the underlying A.R.C., theA.R.C. must be removed to expose the underlying integrated circuitsubstrate for subsequent modification as mentioned above. Commonly, theA.R.C. is removed using a reactive ion etch process, however, othertypes of dry etching or wet etching as known to those skilled in the artmay be used.

Bottom antireflective coatings (B.A.R.C.s) generally come in twoclasses, the developer soluble class in which the B.A.R.C. is dissolvedin the developer at the time of the resist development, ordeveloper-insoluble B.A.R.C.s in which the image is transferred throughthe B.A.R.C. in a dry etch step. The developer soluble B.A.R.C.s aretypically materials that are slightly soluble in the developer anddissolve isotropically as soon as the resist above them dissolves duringthe development process. The logical consequence of this is that thereis significant undercutting of the resist as the B.A.R.C. dissolves awayunderneath it, and there is a sloped B.A.R.C. edge profile. Theundercutting and sloped profile promote lift-off of small resistfeatures and limits the resolution of such B.A.R.C.s. Thus currentlyavailable developer soluble B.A.R.C.s do not have the needed highresolution (e.g., in the sub-quarter micron range) and do not meet theneeds of processes such as shallow implants, described below. Therefore,all high resolution B.A.R.C.s that are currently used are developerinsoluble. Thus, generally inorganic B.A.R.C.s are of the developerinsoluble class, as are most of the high resolution organic B.A.R.C.s.The reason for this has been set forth above—i.e., due to the problem ofavoiding footing or undercuts with what is essentially an isotropic wetetch process of the B.A.R.C. Even if the B.A.R.C. dissolution rate isexactly matched to that of the resist in the correct exposure state forimagewise printing, an undercut-free and foot free, vertical profile isachieved at best only for an infinitesimally short moment. While thiscan be accepted for larger features; this behavior leads to a lowprocess latitude for high resolution imaging (see FIG. 1).

For a number of applications, e.g., for shallow implants, it isdesirable to avoid damage to the substrate by plasma processing. At thesame time, control of reflections from the surface and control of theswing curve may make the use of a B.A.R.C. desirable. These technicalrequirements together can be met by the use of a developer-solubleB.A.R.C., but not if high resolution, e.g., in the sub-quarter micronregion, is desired. Currently, there appear to be no B.A.R.C.s that bothavoid dry etching and provide sufficient resolution for the abovementioned applications.

The present invention resolves this impasse by providing a first minimumB.A.R.C. that is developed at the time of resist development. Itresolves the issue of poor sidewall control by using a photosensitiveB.A.R.C., or, expressed in an alternative way, a highly dyed photoresiston which a second photoresist imaging layer can be applied without orwith only minimal intermixing. The photosensitive B.A.R.C. of theinvention is exposed during the photoresist exposure step; there is nosecond exposure step following the photoresist development. The exposureof the B.A.R.C. to light generates a solubility gradient in the B.A.R.C.that makes it possible to achieve an anisotropic component in theB.A.R.C. dissolution, as opposed to the isotropic development ofconventional developer-soluble B.A.R.C.s.

U.S. Pat. No. 6,110,653, issued Aug. 29, 2000, to inventors Holmes etal., discloses a method comprising the steps of applying a radiationadsorbing layer on a substrate and forming an acid sensitive, waterinsoluble A.R.C. therefrom, applying a photo patterning resist (PPR)layer on the A.R.C., exposing part of the PPR layer to actinicradiation, developing the PPR layer to form a resist image, renderingthe A.R.C. water soluble, and developing the A.R.C. to uncover selectedportions of the substrate.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 illustrates different types of antireflective bottom coats.

FIG. 2 is an example for near-optimal B.A.R.C.s for 1^(st) and secondminimum applications. n and k values for resist: 1.7043, 0.0071;B.A.R.C.: 1.68, 0.60 (left) and 0.30 (right), substrate (Si): 0.95,2.64. Exposure wavelength: 193 nm.

FIG. 3 shows second minimum B.A.R.C. simulation results, indicatingpresence of a standing wave node in the B.A.R.C. at approximately λ/(2n)film thickness.

FIG. 4 shows first minimum B.A.R.C. simulation results, indicatingabsence of a standing wave node in the latent images.

FIG. 5 illustrates the geometrical locus of an etch front given bysuperposition of spheres. The figure on the left shows wet etching oflayer of isotropic material protected by photoresist. The figure on theright shows etching to remove the entire film depth.

SUMMARY OF THE INVENTION

The present invention provides a process for forming an image on asubstrate, comprising the steps of:

(a) coating on a substrate a first layer of a radiation sensitiveantireflective composition;

(b) coating a second layer of a photoresist composition onto the firstlayer of the antireflective composition;

(c) selectively exposing the coated substrate from step (b) to actinicradiation; and

(d) developing the exposed coated substrate from step (c);

wherein both the photoresist composition and the antireflectivecomposition are exposed in step (c); both are developed in step (d)using a single developer; wherein the antireflective composition of step(a) is a first minimum bottom antireflective coating (B.A.R.C.)composition, having a solids content of up to about 8% solids, and amaximum coating thickness of the coated substrate of λ/2n wherein λ isthe wavelength of the actinic radiation of step (c) and n is therefractive index of the B.A.R.C. composition.

DETAILED DESCRIPTION OF THE INVENTION

The present invention provides a process for forming an image on asubstrate, comprising the steps of:

(a) coating on a substrate a first layer of a radiation sensitiveantireflective composition;

(b) coating a second layer of a photoresist composition onto the firstlayer of the antireflective composition;

(c) selectively exposing the coated substrate from step (b) to actinicradiation; and

(d) developing the exposed coated substrate from step (c);

wherein both the photoresist composition and the antireflectivecomposition are exposed in step (c); both are developed in step (d)using a single developer; wherein the antireflective composition of step(a) is a first minimum bottom antireflective coating (B.A.R.C.)composition, having a solids content of up to 8% solids and a maximumcoating thickness of the coated substrate of λ/2n wherein λ is thewavelength of the actinic radiation of step (c) and n is the refractiveindex of the B.A.R.C. composition.

As used herein, “first minimum B.A.R.C. composition” refers to aB.A.R.C. composition, where the B.A.R.C. coating thickness is close tothe film thickness value that corresponds to the first minimum value ina standard plot of normalized (i.e., relative) reflectance or normalizedsquare root of reflectance versus film thickness. (See, for example,FIG. 2). Such curves are well known to those of ordinary skill in theart, and can be plotted using equations well known to those of ordinaryskill in the art. Similarly, “second minimum B.A.R.C. composition”refers to a composition wherein the coating thickness is close to thefilm thickness corresponds to the second minimum value in the standardplot described above.

Through Brunner's equation (T. Brunner, Proc. SPIE 1466, 297 (1991)), itis possible to ratio the swing amplitudes for a given thickness db ofthe bottom coat to that of the substrate without bottom coat (d_(b)=0).In this way, the swing amplitude reduction S_(rel) relative to thesubstrate is obtained as the square root of the ratio of thereflectivities into the resist. Similarly, one can define S_(rel) formultiple thin film stacks versus the substrate. $\begin{matrix}{{S_{B.A.R.C.}\left( d_{b} \right)} = {4\sqrt{R_{t}{R_{B.A.R.C.}\left( d_{b} \right)}}{\mathbb{e}}^{{- \alpha} \cdot d_{r}}}} \\{S_{Substrate} = {S_{B.A.R.C.}(0)}} \\{= {4\sqrt{R_{t}{R_{B.A.R.C.}(0)}}{\mathbb{e}}^{{- \alpha} \cdot d_{r}}}}\end{matrix}$ $\begin{matrix}{{S_{rel}\left( d_{b} \right)} = \frac{S_{B.A.R.C.}\left( d_{b} \right)}{S_{Substrate}}} \\{= \sqrt{\frac{R_{B.A.R.C.}\left( d_{b} \right)}{R_{B.A.R.C.}(0)}}}\end{matrix}$

In the above equations, S_(B.A.R.C.)(d_(b)) is the swing amplitude ofthe B.A.R.C. layer for a given thickness d_(b); R_(t) is the reflectanceat the top of the resist layer, e.g., to air or to a top antireflectivelayer, R_(B.A.R.C)(d_(b)). is the reflectivity of the B.A.R.C. layer atthickness d_(b); R_(B.A.R.C) (0) is the reflectivity of the substrate(d_(b)=0); α is the resist absorbance, and d_(r) is the resistthickness.

The maximum thickness of the first minimum B.A.R.C. layer is λ/2nwherein λ is the wavelength of the actinic radiation used to expose thecoated substrate, and n is the refractive index of the B.A.R.C.composition. In one embodiment, the first minimum B.A.R.C. compositionhas a maximum coating thickness of 50 nanometers (nm) for 157 and 193 nmexposures, and in one embodiment, 70 nm for 248 nm exposure, and in oneembodiment 120 nm for 365 nm exposure.

In one embodiment of the present invention, the radiation sensitiveantireflective composition and the photoresist composition comprise apositive-working composition wherein the antireflective and thephotoresist compositions are initially insoluble in the developer butare rendered developer-soluble upon exposure to actinic radiation.

In one embodiment, the radiation sensitive antireflective compositionand the photoresist composition comprise a negative-working compositionwherein the antireflective and the photoresist compositions areinitially soluble in the developer but are rendered developer-insolubleupon exposure to actinic radiation.

In one embodiment, the B.A.R.C. composition is substantially free ofcross-linking and is insoluble in the photoresist solvent (i.e., thesolvent used in the photoresist composition that is used in step (b) ofthe present invention. The coating of the second layer of thephotoresist composition in step (b) is typically conducted using asolution of photoresist composition in a suitable photoresist solvent).Suitable photoresist solvents include propylene glycol methyl etheracetate (PGMEA), 3-methoxy-3-methyl butanol, 2-heptanone (methyl amylketone), propylene glycol methyl ether (PGME), ethylene glycolmonomethyl ether, ethylene glycol monoethyl ether, diethylene glycolmonoethyl ether, ethylene glycol monoethyl ether acetate, ethyleneglycol monomethyl acetate, or a monooxymonocarboxylic acid ester, suchas methyl oxyacetate, ethyl oxyacetate, butyl oxyacetate, methylmethoxyacetate, ethyl methoxyacetate, butyl methoxyacetate, methylethoxyacetate, ethyl ethoxyacetate, ethoxy ethyl propionate, methyl3-oxypropionate, ethyl 3-oxypropionate, methyl 3-methoxypropionate,ethyl 3-methoxypropionate, methyl 2-oxypropionate, ethyl2-oxypropionate, ethyl 2-hydroxypropionate (ethyl lactate (EL)), ethyl3-hydroxypropionate, propyl 2-oxypropionate, methyl 2-ethoxypropionate,propyl 2-methoxy propionate, and mixtures thereof.

In one embodiment, the process of the present invention, furthercomprises baking the coated substrate of step (a) (i.e., the substratecoated with the first minimum B.A.R.C. composition) at a temperature of40° C. to 240° C., and in one embodiment, 90° C. to 150° C., and in oneembodiment 100° C. to 130° C. for a period of time less than 3 minutesprior to step (b). While such a baking step that introduces cross linksis not excluded from the scope of the present invention, it ispreferable that such a baking step is substantially free ofcross-linking steps, i.e., the baking process preferably does notsubstantially introduce crosslinking in the first minimum B.A.R.C.composition.

A B.A.R.C. acts as an interference device, a so-called Fabry-Perotetalon. As such, there will be a sequence of maxima and minima in thereflectance, the position and height of which depends on the opticalconstants of B.A.R.C., resist, and substrate as well as the exposurewavelength. An example for the interference behavior of a B.A.R.C. isgiven in FIG. 2 for two materials which have near-optimal opticalconstants for operation near the first and second interference minima.The intensity of the standing wave in the resist depends in a complexway on reflectivity, whereas the amplitude of the swing curve depends onthe square root of the reflectivity. The plots in FIG. 2 show materialswith different absorbances. In the plot on the left, the absorbance ofthe B.A.R.C. composition is very high, so that the thickness at or nearthe first minimum is the preferred operating thickness. In the plot onthe right, a B.A.R.C. composition is used with lower absorbance, onethat makes it appropriate for use at a thickness that corresponds to ornear a second minimum. For developer insoluble B.A.R.C.s, the preferredoperating region is frequently at or near the second minimum, whichgives better tolerance to thickness variations of the B.A.R.C.composition and to topography in the substrate.

The first minimum B.A.R.C. composition of the present invention can beof any chemical composition provided it has the presently claimedproperties. Typically A.R.C. compositions contain a dye moiety that mayor may not be polymer bound. Some common examples of suitable dyes(including both polymer-bound and non polymer-bound dyes, i.e., dyes notbound to a polymer) are substituted and unsubstituted aromatic compoundssuch as substituted or unsubstituted styrenes, acetoxystyrenes,naphthalenes (e.g., naphthol AS, naphthol ASBI), chirorostyrene,nitrostyrene, benzyl methacrylate or acrylate, hydroxybenzophenones,anthracenes (e.g., 9-methylanthracene), bisphenyls (includinghydroxybisphenols), methine dyes, anthraquinones, and hydroxysubstitutedaromatic azo dyes. Substituted and unsubstituted heterocyclic aromaticrings containing heteroatoms such as oxygen, nitrogen, sulfur, orcombinations thereof can also be used. Some examples of theseheterocyclic dyes include acridines, pyrazoles, pyrrazolines,imadazoles, pyrrolidines, pyrans, piperidines, and quinolines. Someexamples of dye-containing monomers that can be used to make thepolymer-bound dyes include N-methylmaleimide, 9-anthrylmethylmethacrylate, benzyl methacrylate, hydroxystyrene, vinyl benzoate, vinyl4-tert-butylbenzoate, ethylene glycol phenyl ether acrylate,phenoxypropyl acrylate, 2-(4-benzoyl-3-hydroxyphenoxy)ethyl acrylate,2-hydroxy-3-phenoxypropyl acrylate, phenyl methacrylate,9-anthracenylmethyl methacrylate, 9-vinylanthracene, 2-vinyinaphthalene,N-vinylphthalimide, N-(3-hydroxy)phenyl methacrylamide,N-(3-hydroxy-4-hydroxycarbonylphenylazo)phenyl methacrylamide,N-(3-hydroxyl-4-ethoxycarbonylphenylazo)phenyl methacrylamide,N-(2,4-dinitrophenylaminophenyl) maleimide,3-(4-acetoaminophenyl)azo-4-hydroxystyrene,3-(4-ethoxycarbonylphenyl)azo-acetoacetoxy ethyl methacrylate,3-(4-hydroxyphenyl)azo-acetoacetoxy ethyl methacrylate, andtetrahydroammonium sulfate salt of 3-(4-sulfophenyl)azoacetoacetoxyethyl methacrylate. Dyes described in U.S. Pat. Nos. 6,114,085,5,652,297, 5,981,145, and 6,187,506 can also be used. Specific examplesof non-polymer bound dyes include coumarin 7, coumarin 138, coumarin314, curcumin, and Sudan Orange G, and 9-anthracenemethanol.Polymer-bound dyes can be any light absorbing composition that absorbslight at the wavelength of interest. It is preferable that suchpolymer-bound dyes do not crosslink under the processing conditions,although polymer-bound dyes that can be crosslinked are also includedwithin the scope of the present invention.

The final chemical structure of the polymer-bound dye can be optimizedby having those types and ratios of monomeric units (i.e., lightabsorbing dye-containing monomers) that give the desired properties forthe antireflective coating; for example, wavelength of absorption,intensity of absorption, solubility characteristics, refractive index,and coating properties. The wavelength of the polymer of theantireflective coating is matched to that of the irradiation wavelength.Typically, these wavelengths range from 145 nm to 450 nm, preferably,436 nm and 365 nm for g- and i-line exposures respectively, 248 nm forKrF laser, 193 nm for ArF laser, and 157 nm for F₂ laser. Broadbandexposure units require polymers that absorb over a broad range ofwavelengths. A strongly absorbing polymer prevents light from reflectingback into the photoresist and acts as an effective antireflectivecoating. The choice of comonomers and substituents allows for therefractive index and the absorption wavelength and intensity of thepolymer to be optimized to give the minimum back reflection into thephotoresist. Furthermore, a strongly absorbing polymer allows forthinner coatings to be used beneath the photoresist, thus resulting in abetter image transfer.

Solubility of the polymer bound dyes in solvents of lower toxicity isanother very important characteristic of the present invention. Examplesof such lower toxicity solvents include propylene glycol methyl etheracetate (PGMEA), propylene glycol methyl ether (PGME), ethyl lactate(EL), methyl pyruvate (MP), methyl amyl ketone (MAK), diacetone alcohol,or ethoxyethyl propionate (EEP). However, designing polymers for suchsolubility must take into account the need to prevent intermixing of thebottom antireflective layer and the photoresist. For example, if thepolymer bound dye is soluble in EL but not in PGMEA, then EL is anappropriate solvent for use with a PGMEA based top resist. The use ofwater or mixtures of water and organic solvents, in particular alcohols,is also possible in principle provided that the dissolution rate of theB.A.R.C. in the aqueous base developer is sufficiently slow in theunexposed state and sufficiently high in the exposed, baked andchemically transformed state to generate an essentially non-isotropicdevelopment process. Changing the substituents on the polymer canfurther optimize the solubility characteristics of the polymer.

In one embodiment, the first minimum B.A.R.C. composition of the presentinvention comprises a polymer derived from monomers comprising mevaloniclactone methacrylate (MLMA), and in one embodiment monomers comprising2-methyladamantyl methacrylate (MAdMA). In one embodiment, the polymeris a terpolymer of N-methylmaleimide, MLMA, and MAdMA.

The process used for polymerization to prepare the polymers for thefirst minimum B.A.R.C. composition of the present invention can be anyof the ones known in the art for polymerizing vinyl/acrylic monomers,such as, ionic, free radical, or coordination polymerization. Thepolymer structure formed can be composed of alternate, block or randomcopolymers. The weight average molecular weight of the polymer rangesfrom about 500 to about 50,000 and in one embodiment from 1,000 to40,000 and in one embodiment from 2,000 to 20,000.

The mole % of the dye containing monomer can range from about 5 to 95%,and the mole % of the comonomer or comonomers can range from about 5 toabout 95% in the final polymer. Additionally, the polymer may containunreacted precursors and/or monomers from the synthetic steps of thepreparation of the polymer. The dye functionality can be incorporated inthe monomer prior to polymerization or reacted with the polymer afterpolymerization.

The first minimum B.A.R.C. compositions of the present invention cancomprise additional optional components that may be added to enhance theperformance of the B.A.R.C. composition or the final image. Suchcomponents include surface levelling agents, adhesion promoters,antifoaming agents, etc. The absorption of the antireflective coatingcan be optimized for a certain wavelength or ranges of wavelengths bythe suitable choice of substituents on the dye functionality. Usingsubstituents that are electron withdrawing or electron donatinggenerally shifts the absorption wavelength to longer or shorterwavelengths respectively. In addition, the solubility of theantireflective polymer in a particularly preferred solvent can beadjusted by the appropriate choice of substituents on the monomers.

The first minimum B.A.R.C. compositions of the present invention have asolids content of up to 8% solids, and in one embodiment up to 6%, andin one embodiment up to 2% solids. The exact weight used is dependent onthe molecular weight of the polymer(s) and other components used to makethe B.A.R.C. composition, and the film thickness of the coating desired.Typical solvents, used as mixtures or alone, that can be used are PGME,PGMEA, EL, cyclopentanone, cyclohexanone, hexanone, and gammabutyrolactone.

Since the antireflective film is coated on top of the substrate and maybe further subjected to dry etching, it is envisioned that the film isof sufficiently low metal ion level and purity that the properties ofthe semiconductor device are not adversely affected. Treatments such aspassing a solution of the B.A.R.C. composition through an ion exchangecolumn, filtration, and extraction processes can be used to reduce theconcentration of metal ions and to reduce particles.

The antireflective coating composition is coated on the substrate usingtechniques well known to those skilled in the art, such as dipping, spincoating or spraying. As disclosed above, the coating may be furtherheated on a hot plate or convection oven to remove any residual solvent,to introduce crosslinking (if desired) or for further processing ifdesired.

Photoresist compositions to be coated on top of the B.A.R.C. layer canbe any of the types used in the semiconductor industry provided thesensitivity of the photoactive compound in the photoresist matches thatof the antireflective coating.

There are two types of photoresist compositions, negative-working andpositive-working. When negative-working photoresist compositions areexposed image-wise to radiation, the areas of the resist compositionexposed to the radiation become less soluble to a developer solution(e.g. a cross-linking reaction occurs) while the unexposed areas of thephotoresist coating remain relatively soluble to such a solution. Thus,treatment of an exposed negative-working resist with a developer causesremoval of the non-exposed areas of the photoresist coating and thecreation of a negative image in the coating, thereby uncovering adesired portion of the underlying substrate surface on which thephotoresist composition was deposited.

On the other hand, when positive-working photoresist compositions areexposed image-wise to radiation, those areas of the photoresistcomposition exposed to the radiation become more soluble to thedeveloper solution (e.g. a rearrangement reaction occurs) while thoseareas not exposed remain relatively insoluble to the developer solution.Thus, treatment of an exposed positive-working photoresist with thedeveloper causes removal of the exposed areas of the coating and thecreation of a positive image in the photoresist coating. Again, adesired portion of the underlying surface is uncovered.

Positive working photoresist compositions are currently favored overnegative working resists because the former generally have betterresolution capabilities and pattern transfer characteristics.Photoresist resolution is defined as the smallest feature, which theresist composition can transfer from the photomask to the substrate witha high degree of image edge acuity after exposure and development. Inmany manufacturing applications today, resist resolution on the order ofless than one micron are necessary. In addition, it is almost alwaysdesirable that the developed photoresist wall profiles be near verticalrelative to the substrate. Such demarcations between developed andundeveloped areas of the resist coating translate into accurate patterntransfer of the mask image onto the substrate. This becomes even morecritical as the push toward miniaturization reduces the criticaldimensions on the devices.

Positive-acting photoresists comprising novolak resins andquinone-diazide compounds as photoactive compounds are well known in theart. Novolak resins are typically produced by condensing formaldehydeand one or more multi-substituted phenols, in the presence of an acidcatalyst, such as oxalic acid. Photoactive compounds are generallyobtained by reacting hydroxyphenolic compounds with naphthoquinonediazide acids or their derivatives. The sensitivity of these types ofresists typically ranges from about 350 nm to 440 nm.

Photoresists sensitive to short wavelengths, between about 145 nm andabout 350 nm can also be used. These resists, sensitive around 248 nm,normally comprise polyhydroxystyrene or substituted polyhydroxystyrenederivatives, a photoactive compound (including a photoacid generator inthe case of a chemically amplified system), and optionally a solubilityinhibitor. The following references exemplify the types of photoresistsused: U.S. Pat. No. 4,491,628, U.S. Pat. No. 5,069,997 and U.S. Pat. No.5,350,660.

Similarly, resists sensitive around 193 nm can also be used. Examples of193 nm resists include polyacrylates or polymethacrylates, copolymersbased on cycloolefins (such as norbornene, tetracyclooctadecene andderivatives of these monomers) and maleic anhydrides, and hybridcopolymers or mixtures of copolymers based on cycloolefins, maleicanhydrides and acrylates/methacrylates.

After coating the substrate with the B.A.R.C. composition of the presentinvention, and baking the coated substrate, an edge bead remover may beapplied to clean the edges of the coated substrate using processes wellknown in the art. The preferred range of temperature is from about 70°C. to about 140° C. A film of photoresist is then coated on top of theantireflective coating and baked to substantially remove the photoresistsolvent, or for other processing. Thus, in one embodiment, the presentinvention further comprises baking the coated substrate of step (c)prior to step (d). In one embodiment, this baking temperature rangesfrom 80° C. to 150° C. The substrate with the coated B.A.R.C. layer andphotoresist layer is imagewise exposed and developed in an aqueousdeveloper to remove the exposed (for positive photoresist) oralternatively unexposed (for negative photoresist). Preferably thedeveloper is an aqueous basic developer, such as an aqueous metal ionfree hydroxide. Suitable examples of such metal ion free hydroxideinclude tetraalkylammonium hydroxides (such as tetramethylammoniumhydroxide). An optional heating step can be incorporated into theprocess prior to development and after exposure. The process of coatingand imaging photoresists is well known to those skilled in the art andis optimized for the specific type of resist used. If necessary, thepatterned substrate can then be dry etched in a suitable etch chamber toremove any remaining traces of the antireflective film, with theremaining photoresist acting as an etch mask.

In one embodiment of the present invention, the image produced by theclaimed process is substantially free of undercutting and footing. Whilenot wishing to be bound by theory, it is believed that this is due tothe presence of an anisotropic component (introduced by actinicradiation) in the B.A.R.C. dissolution. This can be illustrated by thefollowing. In the case of a non-photosensitive developer-soluble bottomantireflective coatings (not of the present invention), if aphotosensitive layer is used on top of such a B.A.R.C. composition, thestructure defined in it will act as a wet etch mask for the bottomlayer. It is instructive to compare the present invention to suchnon-photosensitive developer-soluble B.A.R.C. compositions and to theclassical process of wet etching (no B.A.R.C. present). In classical wetetching, for example etching of silicon dioxide with diluted hydrogenfluoride solutions, the photoresist structure is defined first usingaqueous base developer. The bottom layer is subsequently etchedisotropically, i.e., the etch rate is the same in all directions. If theetchant has dissolved a thickness “d” of the silicon dioxide in thevertical direction, it will also have dissolved a thickness “d” in thehorizontal direction. In a first approximation, the geometrical locus ofthe etch front is given by the superposition of spheres at the initialetchant/silicon dioxide interface, where the radius of the spheres isgiven by r=v t, where v is the etch rate (with dimensions onlength/time) and t is the etch time (see FIG. 5). It is clear that sucha process will always result in an undercut and is not suitable for,e.g., very fine lines, which will topple if the undercut exceeds acritical value.

In the case of a photoresist on a non-photosensitive butdeveloper-soluble B.A.R.C., the situation is different in that thephotoresist development and the B.A.R.C etching occur in one step, sincethe aqueous base developer performs both functions. The development of ahigh-contrast photoresist proceeds quickly in the center where theaerial image intensity is highest. The development front will reach thebottom of the resist and then proceed to develop the resist mostlysideways. In the case of a developer-soluble B.A.R.C, isotropic etchingof the B.A.R.C will begin as soon as the developer front reaches theresist/B.A.R.C. interface. A new spherical etch front will spread outthrough the B.A.R.C. from the initial point of contact, and additionalspherical etch fronts will be generated in the exposed area as theresist gradually clears away from the B.A.R.C. surface. All of theB.A.R.C. etching is still isotropic, but now the areas at the edge ofthe resist feature clear at a much later time, so that the B.A.R.C. nearthem is exposed to the developer for a shorter time. Since these areascontributed the most to the undercut in the above example of the wetetching of a silicon dioxide layer, it is possible to improve on theamount of underetch of a developer-soluble B.A.R.C. relative to thesituation in the silicon dioxide example. However, in practice, it isstill difficult to achieve images that are free of either footing orundercutting, since due to the isotropic nature of the B.A.R.C. etch thetransition from footing to undercutting occurs in a very short time.This makes the developer-soluble B.A.R.C. process inherently unstable.

The photosensitive B.A.R.C. of the present invention provides a stableprocess with which undercut or footing can be prevented by providing astrong anisotropic component in the B.A.R.C. etch. The B.A.R.C. issubjected to the same aerial image as the photoresist, and it will behighly soluble in the center of the exposed area, while remaininginsoluble in the dark area. In other words, there will be a negativelateral gradient in solubility from the center of the open feature toits edge. As it does in a photoresist, the development will slow downand essentially stop as the development front progresses from the centerto the edge of the exposed area. With proper adjustment of the processconditions, this makes it possible to achieve a stable process thatresults in an image that is free of both footing and undercutting. Thefollowing specific examples will provide detailed illustrations of themethods of producing and utilizing compositions of the presentinvention. These examples are not intended, however, to limit orrestrict the scope of the invention in any way and should not beconstrued as providing conditions, parameters or values which must beutilized exclusively in order to practice the present invention.

EXAMPLES Synthesis and Performance Examples Example 1

To a 250 mL 4 neck flask equipped with a condenser, a thermometer, anitrogen inlet, and a mechanical stirrer were added benzyl methacrylate(6.5 g; 0.037 moles), methacrylate ester of mevalonic lactone (MLMA)(13.5 g; 0.068 mole), azobisisobutylnitrile (AIBN) (3 g) andtetrahydrofuran (THF) (50 g). A solution was obtained and was degassedfor 10 minutes. The reaction was refluxed for 6 hours then drowned into600 mL of hexane. The precipitated polymer was filtered and dried. Thepolymer was next dissolved in 60 g of cyclopentanone and then slowlyadded to 600 mL of methanol to reprecipitate. The polymer was filtered,rinsed and dried. The reprecipitated polymer was redissolved in 60 g ofcyclopentanone and then precipitated again into 600 mL of methanol. Thepolymer was filtered, rinsed and dried. The polymer coating hadrefractive indices n and k of 1.85 and 0.34 respectively at 193 nm asmeasured by a J. A. Woollam WVASE 32™ Ellipsometer.

Example 2 (Comparative Example)

To the polymer (3.45 wt %) from Example 1 prepared above were addedtriphenylsulfonium nonaflate (0.00871 wt %), tridecylamine (0.0034 wt%), trismethoxyethoxyethylamine (0.123 wt %), Fluorad™ FC-4430 (0.10 wt%) (a fluorosurfactant available from 3M) and ethyl lactate (96.5 wt %).The solution was mixed and filtered through a 0.1 micrometer (μm)filter.

A silicon wafer was coated first with 780 Å (78 nm) of the aboveB.A.R.C. solution with a softbake (SB) 110° C./60 seconds. Next B.A.R.C.coated wafer was coated with 3300 Å of AZ® EXP AX2020P resist (acommercial photoresist comprising a copolymer derived from a hybridacrylate, cycloolefin, and maleic anhydride; available from AZElectronic Materials Business Unit of Clariant Corporation), using a130° C./60 second SB. The coated wafer was exposed using an ISI 193 nmministepper. The exposed wafer had a post exposure bake (PEB) of 60seconds at 120° C. with a puddle development of 60 seconds of AZ® 300MIF Developer (an aqueous solution of tetramethylammonium hydroxideavailable from AZ Electronic Materials Business Unit of ClariantCorporation). The results showed that for 0.18 μm lines, the resist wasover exposed but the B.A.R.C. was not completely removed.

Example 3 (Comparative Example)

To the polymer (3.46 wt %) from Example 1 prepared above were addedtriphenylsulfonium nonaflate (0.0340 wt %), trimethylsulfonium hydroxide(0.0035 wt %), Fluorad™ FC-4430 (0.10 wt %), and ethyl lactate (96.5 wt%). The solution was mixed and filtered through a 0.1 μm filter.

A silicon wafer was coated first with 600 Å (60 nm) of the aboveB.A.R.C. solution with a SB 110° C./60 seconds. Next B.A.R.C. coatedwafer was coated with 3300 Å (330 nm) of AZ® EXP AX1050P (a commercialphotoresist comprising a polymethacrylate; available from AZ ElectronicMaterials Business Unit of Clariant Corporation, as a solution in PGMEA)resist using a bake of 130° C./60 second. The coated wafer was exposedusing a ISI 193 nm ministepper. The exposed wafer had a PEB of 60seconds at 120° C. with a puddle development of 60 seconds of AZ® 300MIF Developer. The results show that for 0.18 μm lines, 23millijoules/cm² (mJ/cm²) was required to clear these isolated lines. TheB.A.R.C. layer at dense lines was not opened up even up to 25 mJ/cm² andthe resist was grossly over exposed.

Example 4

A B.A.R.C. solution was prepared as follows. To the polymer (1.77 wt %)prepared above in Example 1 were added triphenylsulfonium nonaflate(0.0270 wt %), tridecylamine (0.0023 wt %), Fluorad™ FC-4430 (0.10 wt%), and ethyl lactate (98.2 wt %). The resulting solution was filteredthrough a 0.1 μm filter.

A silicon wafer was coated with the 300 Å (30 nm) of the above B.A.R.C.solution using a SB 110° C./60 seconds. Next B.A.R.C. coated wafer wascoated with 3300 Å (330 nm) of AZ® EXP AX2020P resist using a SB of 130°C./60 seconds. The coated wafer was exposed using an ISI 193 nmministepper. The exposed wafer had a PEB of 60 seconds at 120° C. with apuddle development of 60 second of AZ® 300 MIF Developer.

In contrast the results showed that 11 mJ/cm² was required to cleanlyopen 0.18 μm isolated lines. The lines in contrast were well formed andnot over exposed. The dense lines (1:1) cleared at 17 mJ/cm² with cleanwell-shaped dense 1:1 lines.

Example 5

A B.A.R.C. solution was prepared as follows. To the polymer (1.77 wt %)prepared above in Example 1 was added of triphenylsulfonium nonaflate(0.0270 wt %), adamantamine (0.0028 wt %), Fluorad™ FC-4430 (0.10 wt %),and ethyl lactate (98.2 wt %). The resulting solution was filteredthrough a 0.1 μm filter.

A silicon wafer was coated with the 300 Å (30 nm) of the above B.A.R.C.solution using a SB 110° C./60 seconds. Next B.A.R.C. coated wafer wascoated with 3300 Å (330 nm) of AZ® EXP AX2020P resist using a SB of 130°C./60 seconds. The coated wafer was exposed using an ISI 193 nmministepper. The exposed wafer had a PEB of 60 seconds at 120° C. with apuddle development of 60 second of AZ® 300 MIF Developer.

In contrast the results show that 13 mJ/cm² was required to cleanly open0.18 μm isolated lines. The dense lines (1:1) cleared at 21 mJ/cm².

Example 6

A B.A.R.C. solution was prepared as follows. To the polymer (1.77 wt %)prepared above in example 1 was added of triphenylsulfonium nonaflate(0.0270 wt %), trimethylsulfonium hydroxide (0.0023 wt %), Fluorad™FC-4430 (0.10 wt %), and ethyl lactate (98.2 wt %). The resultingsolution was filtered through a 0.1 μm filter.

A silicon wafer was coated with the 300 Å (30 nm) of the above B.A.R.C.solution using a SB 110° C./60 seconds. Next B.A.R.C. coated wafer wascoated with 3300 Å (330 nm) of AZ® EXP AX2020P resist using a SB of 130°C./60 seconds. The coated wafer was exposed using an ISI 193 nmministepper. The exposed wafer had a PEB of 60 seconds at 120° C. with apuddle development of 60 second of AZ® 300 MIF Developer.

In contrast the results show that 15 mJ/cm² was required to cleanly open0.18 μm isolated lines. The dense lines open even up to 15 mJ/cm².

Comparison of Examples 4, 5, and 6 (utilizing first minimum B.A.R.C.s)with Examples 2 and 3 (utilizing second minimum B.A.R.C.) reveals anadvantage in going from second minimum to first minimum. At secondminimum, the B.A.R.C. and resist would not image well. At first minimumthe combination imaged well and functioned well as a B.A.R.C., reducingstanding waves.

Example 7 (Comparative Example)

A silicon wafer was coated first with 3300 Å of AZ® EXP AX2020P resistusing a SB of 110° C./60 seconds (No B.A.R.C. was used). An ISI 193 nmministepper was used for exposure. The exposed wafer had a PEB of 90seconds at 130° C. with a development using 30-second puddle of AZ® 300MIF. The optimum dosage for dose to print was used. The example clearlyshowed more standing waves.

Example 8

To a 250 ml, 4 neck flask equipped with a condenser, a thermometer, anitrogen gas inlet and mechanical stirrer were added the methacrylateester of 9-anthracene methanol (AMMA) (6.4 g, 0.0227 mole), MLMA (8.6 g,0.0434 mole), AIBN (3 g) and cyclopentanone (40 g). A solution wasobtained and was degassed for 10 minutes. The reaction was refluxed for4.5 hours then drowned into 600 ml of hexane. The precipitated polymerwas filtered and dried.

To the polymer (0.26 g) above were added triphenylsulfonium nonaflate(0.016 g), Fluorad™ FC-4430 (0.01 g) and 9.73 g of ethyl lactate. The(2.6% solids) solution was mixed and filtered through a 0.1 μm filter.

A silicon wafer was coated first with 600 Å (60 nm) of the preparedB.A.R.C. solution and softbaked at 110° C./60 seconds. Next the B.A.R.C.coated wafer was coated with 6310 Å (631 nm) of AZ® DX5200P photoresist(a hybrid acetal resist available from AZ Electronic Materials BusinessUnit of Clariant Corporation) using a bake of 90° C./60 second. Thecoated wafer was imagewise exposed using an ISI 193 nm ministepper. Theexposed wafer was given a PEB of 60 seconds at 120° C., followed by apuddle development of 60 seconds with AZ® 300 MIF Developer. The SEMresults showed that the B.A.R.C. cleared down to the substrate with adose of 20 mJ/cm2. The B.A.R.C. coating also gave a refractive index andabsorption at 248 nm for n and k of 1.45 and 0.38 respectively asmeasured by a J. A. Woollam WVASE 32™ Ellipsometer.

Simulation Examples

For the present invention, many promising formulations were developedthat showed photosensitivities very similar to the photoresists used fortesting and that seemed to be essentially free of intermixing phenomena.At first all of these formulations were tested at thicknessescorresponding to the second reflectivity minimum of the B.A.R.C. intothe photoresist. The reason for this was that it was deemed to be easierfrom the synthetic side to include fewer highly absorbing units in theB.A.R.C., and as can be seen from FIG. 2, lower absorbance gives betterperformance for the second or higher minima. The experimental resultsconsistently showed that photosensitive second minimum B.A.R.C.s openedlarge features reasonably well but scummed strongly for fine features.The scumming went away at high exposure doses, but for these dosesalready a considerable undercut was observed. Surprisingly, it was foundthat this behavior did not occur when the same B.A.R.C.s were applied ina thickness appropriate for work at the first minimum. The resist thencleaned out well and without scumming even for sub-quarter micronfeatures. In many cases, undercut and footing-free, vertical sidewallwere obtained for which no clear discontinuity in slope could bediscerned between the photoresist and the B.A.R.C..

This surprising and unexpected behavior led to carrying out a simulationof the light distribution and the latent image in the bottom A.R.C. Thisis not usually done for bottom A.R.C.s because it is of no interest forthe non-photosensitive varieties, and it requires modifications orspecial tricks to do this with standard commercial programs. Forexample, with the popular PROLITH/2 simulation program, the photoresistneeds to be defined as a contrast enhancement layer and the B.A.R.C. asa photoresist in order to be able to perform the simulation.

The results of the simulations with PROLITH/2 simulation program showedthat there is a standing wave node in the B.A.R.C. at approximatelyλ/(2n) thickness. This standing wave is still visible even afterdiffusion in a post exposure bake is taken into account (shown in FIG. 3for a chemically amplified B.A.R.C.). The scumming of the photosensitiveB.A.R.C. was the result of this standing wave node and the low amount oflight coupled into the lower part of the B.A.R.C.

In contrast, if a first minimum B.A.R.C. is imaged, its thickness isgiven by a complex formula but it will always be below the λ/(2n)thickness of the standing wave node (possibly excepting transparentsubstrates). The latent image does not exhibit the standing wave node,and the soluble area goes cleanly down the middle of the image,especially after the post exposure bake. As can be seen from thecorresponding simulations (FIG. 4), a first minimum B.A.R.C. ispredicted to open up cleanly down to the substrate, as is indeedobserved experimentally. It is clear from the above that the use of afirst minimum photosensitive B.A.R.C.s has intrinsic imaging advantagesover B.A.R.C.s designed to operate at higher film thicknesses.

Each of the documents referred to above is incorporated herein byreference in its entirety, for all purposes. Except in the Examples, orwhere otherwise explicitly indicated, all numerical quantities in thisdescription specifying amounts and concentrations of materials, reactionand process conditions (such as temperature, time), and the like are tobe understood to be modified by the word “about”.

While the invention has been explained in relation to its preferredembodiments, it is to be understood that various modifications thereofwill become apparent to those skilled in the art upon reading thespecification. Therefore, it is to be understood that the inventiondisclosed herein is intended to cover such modifications as fall withinthe scope of the appended claims.

1-26. (canceled)
 27. A radiation sensitive photoimageable antireflectivecomposition capable of being developed in an aqueous alkaline developercomprising a polymer, where the antireflective coating composition iscapable of forming an antireflective layer below a photoresist layerwith a maximum coating thickness of λ/2n, where λ is wavelength ofexposure and n is refractive index of the antireflective coatingcomposition and a minimum coating thickness greater than zero.
 28. Theantireflection composition of claim 1, where the antireflective layer iscoated over a photoresist layer and the antireflective layer and thephotoresist layer are developed in a single step.
 29. The antireflectivecomposition of claim 1, where the antireflective composition isinitially insoluble in the developer but rendered developer solubleafter exposure to actinic radiation.
 30. The antireflective compositionof claim 1, where the antireflective composition is initially soluble inthe developer but rendered developer insoluble after exposure to actinicradiation.
 31. The antireflective composition of claim 1, furthercomprising a photosensitive compound.
 32. The antireflective compositionof claim 1, where the antireflective layer is capable of forming alatent image.
 33. The antireflective composition of claim 1, where thepolymer comprises a dye.
 34. The antireflective composition of claim 1,further comprising a dye.
 35. The antireflective composition of claim 1,where the dye is polymer-bound.
 36. The antireflective composition ofclaim 1, where the polymer comprises a substituted aromatic moiety or anunsubstituted aromic moiety.
 37. The antireflective composition of claim11, aromatic moiety is selected from anthracene, naphthalene, andheterocyclic ring.
 38. The antireflective composition of claim 11, wherethe aromatic moiety is selected from styrenes, naphthalenes, benzylmethacrylates, anthracenes, bisphenyls, anthraquinones, hydroxylsubstituted aromatic dyes, and heterocyclic aromatics.
 39. Theantireflective composition of claim 1, where the polymer is derived fromat least one monomer selected from N-methylmaleimide, mevaloniclactonemethacrylate (MLMA), 2-methyladamantyl methacrylate (MAdMA), benzylmethacrylate, 9-anthrylmethyl methacrylate (AMMA), styrene,hydroxystyrene, acetoxystyrene, vinyl benzoate, vinyl4-tert-butylbenzoate, ethylene glycol phenyl ether acrylate,phenoxypropyl acrylate, 2-(4-benzoyl-3-hydroxyphenoxy)ethyl acrylate,2-hydroxy-3-phenoxypropyl acrylate, phenyl methacrylate,9-vinylanthracene, 2-vinylnaphthalene, N-vinylphthalimide,N-(3-hydroxy)phenyl methacrylamide,N-(3-hydroxy-4-hydroxycarbonylphenylazo)phenyl methacrylamide,N-(3-hydroxyl-4-ethoxycarbonylphenylazo)phenyl methacrylamide,N-(2,4-dinitrophenylaminophenyl) maleimide,3-(4-acetoaminophenyl)azo-4-hydroxystyrene,3-(4-ethoxycarbonylphenyl)azo-acetoacetoxy ethyl methacrylate,3-(4-hydroxyphenyl)azo-acetoacetoxy ethyl methacrylate, andtetrahydroammonium sulfate salt of 3-(4-sulfophenyl)azoacetoacetoxyethyl methacrylate.
 40. The antireflective composition of claim 1, wherethe antireflective composition is a crosslinkable composition.
 41. Theantireflective composition of claim 1, where the antireflectivecomposition is a non-crosslinkable composition.
 42. The antireflectivecomposition of claim 1, where the solids content of the composition isup to 8% solids. 43 The antireflective composition of claim 1, whereinthe wavelength of exposure ranges from about 145 nm to 450 nm.
 44. Theantireflective composition of claim 11, wherein the wavelength isselected from 365 nm, 248 nm, 193 nm, and 157 nm.
 45. The antireflectivecomposition of claim 1, where the developer is an aqueous solution oftetramethylammonium hydroxide.